A vehicle, for example a car, usually contains a vehicle body lighting system that contains, e.g., the headlights and rear lights of the vehicle. The headlights may, for example, contain high beam headlamps, e.g. for providing the driving lights, as well as light emitting diode modules, e.g., for providing daytime running lights.
For body lighting applications, smart power switches with circuit arrangements may be used that provide switching circuits for switching different current channels of the circuit arrangement, wherein the switching circuits are provided on a single power circuit die shared between the current channels. In order to save die area, the die area occupied by a certain current channel may be located close the die area of another channel, which may create a crosstalk effect in the other circuit or channel. Crosstalk may, for example, be caused by capacitive, inductive, or conductive coupling from one channel to another, and may, for example, limit the capability of the circuit arrangement to drive a high current load, such as a high beam headlamp, and a low current load, such as a light emitting diode (LED) module with the same circuit arrangement.
A circuit arrangement may be arranged to sense a load current by sensing the current through the corresponding current channel on the shared circuit die. In an environment where heavy loads as well as light loads may be switched, the circuit arrangement may contain a power switch capable of being a low on-resistance power switch for the heavy loads and may be able to provide accurate current sense at light loads, such as light emitting diodes (LED). For example, a power switch in an automobile environment may have the ability to drive high-intensity discharge (HID) xenon and halogen lamps and light-emitting diode light sources with a single circuit arrangement, thus improving lighting efficiency and reducing material costs.
As shown in FIG. 1, a prior art current channel 10, which may be connected to voltage source VBAT and ground GND terminals, may be located in a dedicated die area, as indicated by a dashed line, of a shared circuit die, and may contain a switching device 12 and associated current sense circuit and may, for example, be built using MOSFET (metal oxide semiconductor field-effect transistor)-, Trench-FET-, HEMT (high electron mobility transistor)- or IGBT (Insulated-gate bipolar transistor)-technology, just to name a few. The current channel may, for example, contain a power switch. Here, the current sense functionality may be implemented by separating the power switch of the current channel in the (main) switching device 12 and a sense device 14, and by usage of a differential or error amplifier 16 and offset voltage source 17 to form an accurate current sense with an accuracy of the current sense function limited at low load currents, i.e. low currents through switching device 12, by crosstalk encountered when one or more neighbouring current channels (not shown) drive high currents, e.g., having a current strength of more than one Ampere (A). The ratio (Ratio) between IoutX, i.e., the current provided to a load connectable to the OUTX terminal, and the sense current Isense may be given as the resistance RDS(on) between drain and source of the switching device 12 and RDS(on) of the sense device 14 when switched on. A current sense feedback in the shown circuit is formed by the error amplifier 16 and transistor 18. The current sense feedback (negative feedback) may keep voltage potentials at the source terminals of the switching device 12 and sense device 14 equal. This may keep the current through the drain-source path of the sense transistor 14 and of transistor 18 proportional to the load current IoutX provided to output terminal OUTx. As shown, this current may be replicated by replica metal oxide semiconductor field-effect transistors (MOSFET) 20, 22, 24 and may be provided to sense output terminal CSNS with a current gain, which may be Y/X in the shown example.
In order to illustrate the reduction of the sense current accuracy in the current channel shown in FIG. 1 due to the presence of crosstalk effects caused by neighbouring current channels (not shown), an example of a table of channel switching states and corresponding sense current deviation in a third of 5 channels (with a fourth channel permanently switched off) for the prior art sense circuit shown in FIG. 1 is shown in FIG. 2, wherein channels 1 and 2 drive currents of 2A and channel 5 drives a current of 3A, if switched on, whereas the sensed channel 3 provides a low current of 98.6 mA. As can be seen, the sensed current Isense varies, depending on the crosstalk effect caused by the currents flowing through the other channels 1, 2 and 5 sharing the same die or substrate. In the shown example, a relative deviation of the actually sensed current from the correct, undisturbed sense current, where all other channels except the sensed channel 3 are switched off, may be up to 34.89%.
In U.S. Pat. No. 7,852,148, a compensation circuit is shown that is used to improve the accuracy of a current sensing signal for a single channel power FET, using distributed resistances.
In U.S. Pat. No. 6,300,818, a temperature compensation circuit for compensating a temperature dependence of a sensed current of a single channel power switch is shown.
In U.S. Pat. No. 7,190,215, a current sensing, voltage sensing and voltage drop compensation in a single channel device is described.
In U.S. Pat. No. 6,825,626, a current sensing apparatus is described that includes a memory for storing a current sense compensation value based on a difference between the resistance of a sense resistor and an ideal resistance.